1. Field of the Invention
The present invention relates to a viscous fluid coupling for connecting the engine of an automotive vehicle to a cooling fan for an engine radiator, and more particularly, to a viscous fluid coupling of a temperature responsive type in which a bimetal coil located on the exterior of a rotatable casing operates a valve member for controlling the flow of viscous fluid within the casing in response to the temperature of air flow through the engine radiator.
2. Description of the Prior Art
In conventional viscous fluid couplings of this type, a bimetal coil is located on the exterior of a rotatable casing connected to a cooling fan so as to respond to the temperature of air flowing through an engine radiator. The bimetal coil is connected at an outer portion thereof to the casing and is connected at an inner portion thereof to an outer end of a valve shaft which is aligned with the rotational axis of the casing and is rotatably supported within an opening formed in the casing. An inner end portion of the valve shaft is connected to a valve member for controlling the flow of a viscous fluid within the casing. In order to prevent the viscous fluid from leakage, a single sealing ring is provided between the outer periphery of the valve shaft and a wall of the opening of the casing.
In such arrangement, objectionable wear has been experienced on the valve shaft and the wall of the opening of the casing upon use of the coupling. In addition, breakage of the outer end portion of the bimetal coil has occurred upon use of the coupling. The reason why such problems are caused is that the bimetal coil and the valve member resonate due to the vibration transmitted from the engine to the casing and thus exerts radial forces of different magnitude on opposite ends of the valve shaft wherein the valve shaft is slanted largely about a fulcrum of the sealing ring.